In motor applications, an optical encoder or a resolver may be used to determine the angular position of a shaft.
An optical encoder is a device comprising a rotating disk, a light source, and a photodetector (i.e., a light sensor). The disk, which is mounted on the shaft, has coded patterns of opaque and transparent sectors. As the disk rotates, these patterns interrupt the light projected onto the photodetector and generate a digital or pulse signal output that is used to determine the angular position of an object.
A resolver is a rotary transformer comprising a rotor and a stator with one or more windings (i.e., a coil). In response to excitation by one or more source signals, the windings output one or more sine or cosine signals (i.e., output voltages). The magnitude of the sine and cosine signals can be used to determine the angular position of a shaft inserted into the rotor.
Typically, a basic resolver is used for low resolution applications, and a multi-pole resolver is used for high resolution applications. A basic resolver houses two polarity windings in the stator such that the angular position of the shaft is equivalent to the mechanical angle of the stator. A multi-pole resolver houses more than two pole windings in the stator and thus provides more accuracy than a basic resolver.
Unfortunately, existing multi-pole resolvers fail to provide the same accuracy as an optical encoder. In existing multi-pole resolvers, as the rotation of the rotor increases in speed, the magnetic flux around the rotor and the windings distorts the sine and cosine output signals, which decreases the accuracy of angular position measurements.